1. Field of the Invention
The present invention relates generally to automatic transmission apparatus for use in vehicles, and more particularly, to an automatic transmission for a vehicle in which each of plural paths for transmitting the output of an engine is selectively formed through a novel gear train arrangement in accordance with the running condition of the vehicle so as to effect automatically a speed range changing operation.
2. Description of the Prior Art
There has been commonly used in vehicles an automatic transmission employing a planetary gear mechanism. When such an automatic transmission with the planetary gear mechanism is arranged to have the increased number of speed ranges for transmitting power for use in a truck or the like, however, a gear train arrangement provided therein is considerably complicated and the whole configuration thereof is increased in size. Accordingly, there has been proposed such an automatic transmission that uses a gear train arrangement which has been conventionally used in a manual transmission and in which a plurality of gear trains each having a different gear ratio are juxtaposed between a couple of parallel shafts and each of the gear trains is selectively brought into a power transmitting state to provide a plurality of speed ranges, and friction clutch devices provided for conducting the selection of the gear train, in order to achieve automatically a speed range changing operation.
However, with the automatic transmission constituted with such a gear train arrangement and friction clutch devices as described above, the following problems are encountered. In the speed range changing operation, a certain gear train is switched over to a power interrupting state from the power transmitting state, while simultaneously another gear train is switched over to the power transmitting state from the power interrupting state, and at that time, a friction clutch device for the former gear train is required to be disengaged, while another friction clutch device for the latter gear train is required to be engaged. In such case, if the disengagement and engagement of the respective friction clutch devices are not proper in timing, both friction clutch devices may be simultaneously engaged or disengaged and this results in a disadvantage that a so-called changing shock is brought about or an engine which is connected to the automatic transmission is caused to be in a racing condition. Further, in the case where it is intended to control the friction clutch devices to be disengaged and engaged respectively with a proper timing for the purpose of avoiding such a disadvantage, control measures which are extremely complicated may be required.
There has been also proposed a gear type transmission having a plurality of gear trains juxtaposed between a couple of parallel shafts and a clutch arrangement including friction clutch devices and one-way clutch devices operative to cause each of the gear trains to be selectively brought into the power transmitting state, as disclosed in the Japanese patent application published before examination with the publication No. 58/225244. However, this gear type transmission employs a manual synchronizing device as means for causing a gear free from one of the parallel shafts to engage the latter and is constituted with an output shaft thereof provided to be not coaxial with an engine output shaft so as to be used in an automobile of a so-called front engine-front drive type.